For the following exercises, we will also use data from Gapminder; this time on life expectancy.

As per usual, we first need to read in the data. You can just copy, paste and run the following code in(to) your script.

library(readr)

gap_life <- read_csv("../data/gapminder/life_expectancy_years.csv")

Again, the data are currently in wide format.

1

Select only data for the 20th century, but this time use a helper function instead of specifying a range columns.

The helper function you should use here is starts_with(). We also want to keep the country column.

solution 

library(dplyr)

gap_life %>% 
  select(country, starts_with("19"))
## # A tibble: 187 x 101
##    country `1900` `1901` `1902` `1903` `1904` `1905` `1906` `1907` `1908`
##    <chr>    <dbl>  <dbl>  <dbl>  <dbl>  <dbl>  <dbl>  <dbl>  <dbl>  <dbl>
##  1 Afghan~   29.2   29.3   29.3   29.4   29.4   29.5   29.6   29.6   29.7
##  2 Albania   35.5   35.5   35.5   35.5   35.5   35.5   35.5   35.5   35.5
##  3 Algeria   30.1   30.2   30.3   31.3   25.3   28     29.5   29.4   29.3
##  4 Andorra   NA     NA     NA     NA     NA     NA     NA     NA     NA  
##  5 Angola    29.5   29.6   29.7   29.8   29.9   30     30.1   30.1   30.2
##  6 Antigu~   33.7   33.7   33.7   33.7   33.7   33.7   33.7   33.7   33.7
##  7 Argent~   36.6   37.2   37.8   38.3   38.9   39.5   40.2   41     41.7
##  8 Armenia   35.2   35.4   35.6   35.8   36.1   36.3   36.5   36.7   36.9
##  9 Austra~   50     50.5   51.1   51.6   52.1   52.7   53.2   53.7   54.3
## 10 Austria   41.5   42     41     40.1   40.7   41.3   42     42.6   43.2
## # ... with 177 more rows, and 91 more variables: `1909` <dbl>,
## #   `1910` <dbl>, `1911` <dbl>, `1912` <dbl>, `1913` <dbl>, `1914` <dbl>,
## #   `1915` <dbl>, `1916` <dbl>, `1917` <dbl>, `1918` <dbl>, `1919` <dbl>,
## #   `1920` <dbl>, `1921` <dbl>, `1922` <dbl>, `1923` <dbl>, `1924` <dbl>,
## #   `1925` <dbl>, `1926` <dbl>, `1927` <dbl>, `1928` <dbl>, `1929` <dbl>,
## #   `1930` <dbl>, `1931` <dbl>, `1932` <dbl>, `1933` <dbl>, `1934` <dbl>,
## #   `1935` <dbl>, `1936` <dbl>, `1937` <dbl>, `1938` <dbl>, `1939` <dbl>,
## #   `1940` <dbl>, `1941` <dbl>, `1942` <dbl>, `1943` <dbl>, `1944` <dbl>,
## #   `1945` <dbl>, `1946` <dbl>, `1947` <dbl>, `1948` <dbl>, `1949` <dbl>,
## #   `1950` <dbl>, `1951` <dbl>, `1952` <dbl>, `1953` <dbl>, `1954` <dbl>,
## #   `1955` <dbl>, `1956` <dbl>, `1957` <dbl>, `1958` <dbl>, `1959` <dbl>,
## #   `1960` <dbl>, `1961` <dbl>, `1962` <dbl>, `1963` <dbl>, `1964` <dbl>,
## #   `1965` <dbl>, `1966` <dbl>, `1967` <dbl>, `1968` <dbl>, `1969` <dbl>,
## #   `1970` <dbl>, `1971` <dbl>, `1972` <dbl>, `1973` <dbl>, `1974` <dbl>,
## #   `1975` <dbl>, `1976` <dbl>, `1977` <dbl>, `1978` <dbl>, `1979` <dbl>,
## #   `1980` <dbl>, `1981` <dbl>, `1982` <dbl>, `1983` <dbl>, `1984` <dbl>,
## #   `1985` <dbl>, `1986` <dbl>, `1987` <dbl>, `1988` <dbl>, `1989` <dbl>,
## #   `1990` <dbl>, `1991` <dbl>, `1992` <dbl>, `1993` <dbl>, `1994` <dbl>,
## #   `1995` <dbl>, `1996` <dbl>, `1997` <dbl>, `1998` <dbl>, `1999` <dbl>

As you may have already noticed, the dataset comprises some missing data points. Before we start analyzing the data, we might want to know for how many countries we have complete data.

2

Using the dataset in wide format, find out for how many countries we have complete data?

To answer this question you should use the drop_na() function from tidyr.

solution 

library(tidyr)

gap_life %>% 
  drop_na() %>% 
  nrow()
## [1] 184

As in the previous set of data wrangling exercises, we now want to transform the data into the long format.

3

Transform the gap_life dataset into a sensible long format. Name the variable representing the values for life expectancy lifeExp and store the resulting dataframe in a name with the same object as before (gap_life). Also change the type of the year variable to integer.

This is just a repetition from the Tidy Data exercises. What we want to do is to gather the columns with the years into a year variable. To change the variable type, you need to use mutate().

solution 

gap_life <- gap_life %>% 
  gather(-country, key = "year", value = "lifeExp") %>% 
  mutate(year = as.integer(year))

Now let’s apply some of the advanced filtering options we discussed in the Data Wrangling - Part 2 session.

4

Create two new dataframes that include different subets of the gap_life data:

  1. Data for all countries for 1990s (name this one gap_life_1990s),

  2. Data for all years but only for Germany (name this one gap_life_ger).

NB: There are different Germanies in the dataset: West Germany. East Germany, and Germany.

You need to use a helper function from dplyr to create the first new data frame and a specific matching operator to create the second one.

solution 

gap_life_1990s <- gap_life %>% 
  filter(between(year, 1990, 1999))

gap_life_1990s
## # A tibble: 1,870 x 3
##    country              year lifeExp
##    <chr>               <int>   <dbl>
##  1 Afghanistan          1990    51.6
##  2 Albania              1990    73.9
##  3 Algeria              1990    71  
##  4 Andorra              1990    79.5
##  5 Angola               1990    50.2
##  6 Antigua and Barbuda  1990    73.8
##  7 Argentina            1990    72.1
##  8 Armenia              1990    70.2
##  9 Australia            1990    77  
## 10 Austria              1990    75.5
## # ... with 1,860 more rows
gap_life_ger <- gap_life %>% 
  filter(country %in% 
           c("Germany", "West Germany", "East Germany"))

gap_life_ger
## # A tibble: 219 x 3
##    country  year lifeExp
##    <chr>   <int>   <dbl>
##  1 Germany  1800    38.4
##  2 Germany  1801    38.4
##  3 Germany  1802    38.4
##  4 Germany  1803    38.4
##  5 Germany  1804    38.4
##  6 Germany  1805    38.4
##  7 Germany  1806    38.4
##  8 Germany  1807    38.4
##  9 Germany  1808    38.4
## 10 Germany  1809    38.4
## # ... with 209 more rows

For some comparisons (especially via plots), it might help to know which continent the country is located on. For this purpose, we will create a new continent variable. As it would be quite tedious to create this variable manually for all of the countries in the dataset, we will do this only for a subset in this exercise. Just run the following code in your local script to create this subset.

library(dplyr)

gap_life_subset <- gap_life %>% 
  filter(country %in% 
           c("Netherlands", "Brazil", "China", "Algeria", "New Zealand"))

5

Create a continent variable for the countries in gap_life_subset. The variable should be a factor and its values the following: Africa, Americas, Asia, Europe, Oceania.

You should use the case_when() to create this new variable.

solution 

gap_life_subset %>% 
  mutate(continent = factor(case_when(
    country == "Algeria" ~ "Africa",
    country == "Brazil" ~ "Americas",
    country == "China" ~ "Asia",
    country == "Netherlands" ~ "Europe",
    country == "New Zealand" ~ "Oceania")
    ))
## # A tibble: 1,095 x 4
##    country      year lifeExp continent
##    <chr>       <int>   <dbl> <fct>    
##  1 Algeria      1800    28.8 Africa   
##  2 Brazil       1800    32   Americas 
##  3 China        1800    32   Asia     
##  4 Netherlands  1800    39.9 Europe   
##  5 New Zealand  1800    34   Oceania  
##  6 Algeria      1801    28.8 Africa   
##  7 Brazil       1801    32   Americas 
##  8 China        1801    32   Asia     
##  9 Netherlands  1801    39.9 Europe   
## 10 New Zealand  1801    34   Oceania  
## # ... with 1,085 more rows